动态加载外部 javascript 文件，并等待它加载 - 不使用 JQuery

Dynamically load external javascript file, and wait for it to load - without using JQuery

提问by YogevSitton

I'm trying to dynamically load an external .js file (according to an input I get from the user). Currently my code looks like this:

我正在尝试动态加载外部 .js 文件（根据我从用户那里获得的输入）。目前我的代码如下所示：

function createScript(src, id) {
    if (document.getElementById(id) == null) {
        var newScript = document.createElement('script');
        newScript.setAttribute("type", "text/javascript");
        newScript.setAttribute("src", src);
        newScript.setAttribute("id", id);
        document.getElementsByTagName("head")[0].appendChild(newScript);
    }
}

This kind of work. It does load the script, but if I try to call a function that is defined inside the new script it won't work. The weird thing is if I wait for a second (using an alert("test")or something like that) the script does work.

这种工作。它确实加载了脚本，但是如果我尝试调用在新脚本中定义的函数，它将无法工作。奇怪的是，如果我等待一秒钟（使用alert("test")或类似的东西）脚本确实可以工作。

I guess its because the browser adds the <script>tag immediately, but it takes it a little longer to "read" the script inside of the .js file. I tried playing with "typeof testfunction === 'function'"with a few variations but no luck.

我猜是因为浏览器会<script>立即添加标签，但是“读取”.js 文件中的脚本需要更长的时间。我尝试玩"typeof testfunction === 'function'"一些变体，但没有运气。

Any good way of doing this?

有什么好办法吗？

回答by Jason Sebring

February 21, 2017 - how jQuery does it

2017 年 2 月 21 日 - jQuery 是如何做到的

jQuery.getScriptis now just a wrapper for jQuery.get

jQuery.getScript现在只是一个包装 jQuery.get

getScript: function( url, callback ) {
    return jQuery.get( url, undefined, callback, "script" );
}

jQuery.getis just a wrapper of jQuery.ajax– it is defined using metaprogramming as ...

jQuery.get只是一个包装器jQuery.ajax- 它使用元编程定义为......

jQuery.each( [ "get", "post" ], function( i, method ) {
    jQuery[ method ] = function( url, data, callback, type ) {

        // Shift arguments if data argument was omitted
        if ( jQuery.isFunction( data ) ) {
            type = type || callback;
            callback = data;
            data = undefined;
        }

        // The url can be an options object (which then must have .url)
        return jQuery.ajax( jQuery.extend( {
            url: url,
            type: method,
            dataType: type,
            data: data,
            success: callback
        }, jQuery.isPlainObject( url ) && url ) );
    };
} );

jQuery.ajaxis this 430+ LOC monster

jQuery.ajax这是 430+ LOC 怪物吗

ajax: function( url, options ) {

  // If url is an object, simulate pre-1.5 signature
  if ( typeof url === "object" ) {
    options = url;
    url = undefined;
  }

  // Force options to be an object
  options = options || {};

  var transport,

    // URL without anti-cache param
    cacheURL,

    // Response headers
    responseHeadersString,
    responseHeaders,

    // timeout handle
    timeoutTimer,

    // Url cleanup var
    urlAnchor,

    // Request state (becomes false upon send and true upon completion)
    completed,

    // To know if global events are to be dispatched
    fireGlobals,

    // Loop variable
    i,

    // uncached part of the url
    uncached,

    // Create the final options object
    s = jQuery.ajaxSetup( {}, options ),

    // Callbacks context
    callbackContext = s.context || s,

    // Context for global events is callbackContext if it is a DOM node or jQuery collection
    globalEventContext = s.context &&
      ( callbackContext.nodeType || callbackContext.jquery ) ?
        jQuery( callbackContext ) :
        jQuery.event,

    // Deferreds
    deferred = jQuery.Deferred(),
    completeDeferred = jQuery.Callbacks( "once memory" ),

    // Status-dependent callbacks
    statusCode = s.statusCode || {},

    // Headers (they are sent all at once)
    requestHeaders = {},
    requestHeadersNames = {},

    // Default abort message
    strAbort = "canceled",

    // Fake xhr
    jqXHR = {
      readyState: 0,

      // Builds headers hashtable if needed
      getResponseHeader: function( key ) {
        var match;
        if ( completed ) {
          if ( !responseHeaders ) {
            responseHeaders = {};
            while ( ( match = rheaders.exec( responseHeadersString ) ) ) {
              responseHeaders[ match[ 1 ].toLowerCase() ] = match[ 2 ];
            }
          }
          match = responseHeaders[ key.toLowerCase() ];
        }
        return match == null ? null : match;
      },

      // Raw string
      getAllResponseHeaders: function() {
        return completed ? responseHeadersString : null;
      },

      // Caches the header
      setRequestHeader: function( name, value ) {
        if ( completed == null ) {
          name = requestHeadersNames[ name.toLowerCase() ] =
            requestHeadersNames[ name.toLowerCase() ] || name;
          requestHeaders[ name ] = value;
        }
        return this;
      },

      // Overrides response content-type header
      overrideMimeType: function( type ) {
        if ( completed == null ) {
          s.mimeType = type;
        }
        return this;
      },

      // Status-dependent callbacks
      statusCode: function( map ) {
        var code;
        if ( map ) {
          if ( completed ) {

            // Execute the appropriate callbacks
            jqXHR.always( map[ jqXHR.status ] );
          } else {

            // Lazy-add the new callbacks in a way that preserves old ones
            for ( code in map ) {
              statusCode[ code ] = [ statusCode[ code ], map[ code ] ];
            }
          }
        }
        return this;
      },

      // Cancel the request
      abort: function( statusText ) {
        var finalText = statusText || strAbort;
        if ( transport ) {
          transport.abort( finalText );
        }
        done( 0, finalText );
        return this;
      }
    };

  // Attach deferreds
  deferred.promise( jqXHR );

  // Add protocol if not provided (prefilters might expect it)
  // Handle falsy url in the settings object (#10093: consistency with old signature)
  // We also use the url parameter if available
  s.url = ( ( url || s.url || location.href ) + "" )
    .replace( rprotocol, location.protocol + "//" );

  // Alias method option to type as per ticket #12004
  s.type = options.method || options.type || s.method || s.type;

  // Extract dataTypes list
  s.dataTypes = ( s.dataType || "*" ).toLowerCase().match( rnothtmlwhite ) || [ "" ];

  // A cross-domain request is in order when the origin doesn't match the current origin.
  if ( s.crossDomain == null ) {
    urlAnchor = document.createElement( "a" );

    // Support: IE <=8 - 11, Edge 12 - 13
    // IE throws exception on accessing the href property if url is malformed,
    // e.g. http://example.com:80x/
    try {
      urlAnchor.href = s.url;

      // Support: IE <=8 - 11 only
      // Anchor's host property isn't correctly set when s.url is relative
      urlAnchor.href = urlAnchor.href;
      s.crossDomain = originAnchor.protocol + "//" + originAnchor.host !==
        urlAnchor.protocol + "//" + urlAnchor.host;
    } catch ( e ) {

      // If there is an error parsing the URL, assume it is crossDomain,
      // it can be rejected by the transport if it is invalid
      s.crossDomain = true;
    }
  }

  // Convert data if not already a string
  if ( s.data && s.processData && typeof s.data !== "string" ) {
    s.data = jQuery.param( s.data, s.traditional );
  }

  // Apply prefilters
  inspectPrefiltersOrTransports( prefilters, s, options, jqXHR );

  // If request was aborted inside a prefilter, stop there
  if ( completed ) {
    return jqXHR;
  }

  // We can fire global events as of now if asked to
  // Don't fire events if jQuery.event is undefined in an AMD-usage scenario (#15118)
  fireGlobals = jQuery.event && s.global;

  // Watch for a new set of requests
  if ( fireGlobals && jQuery.active++ === 0 ) {
    jQuery.event.trigger( "ajaxStart" );
  }

  // Uppercase the type
  s.type = s.type.toUpperCase();

  // Determine if request has content
  s.hasContent = !rnoContent.test( s.type );

  // Save the URL in case we're toying with the If-Modified-Since
  // and/or If-None-Match header later on
  // Remove hash to simplify url manipulation
  cacheURL = s.url.replace( rhash, "" );

  // More options handling for requests with no content
  if ( !s.hasContent ) {

    // Remember the hash so we can put it back
    uncached = s.url.slice( cacheURL.length );

    // If data is available, append data to url
    if ( s.data ) {
      cacheURL += ( rquery.test( cacheURL ) ? "&" : "?" ) + s.data;

      // #9682: remove data so that it's not used in an eventual retry
      delete s.data;
    }

    // Add or update anti-cache param if needed
    if ( s.cache === false ) {
      cacheURL = cacheURL.replace( rantiCache, "" );
      uncached = ( rquery.test( cacheURL ) ? "&" : "?" ) + "_=" + ( nonce++ ) + uncached;
    }

    // Put hash and anti-cache on the URL that will be requested (gh-1732)
    s.url = cacheURL + uncached;

  // Change '%20' to '+' if this is encoded form body content (gh-2658)
  } else if ( s.data && s.processData &&
    ( s.contentType || "" ).indexOf( "application/x-www-form-urlencoded" ) === 0 ) {
    s.data = s.data.replace( r20, "+" );
  }

  // Set the If-Modified-Since and/or If-None-Match header, if in ifModified mode.
  if ( s.ifModified ) {
    if ( jQuery.lastModified[ cacheURL ] ) {
      jqXHR.setRequestHeader( "If-Modified-Since", jQuery.lastModified[ cacheURL ] );
    }
    if ( jQuery.etag[ cacheURL ] ) {
      jqXHR.setRequestHeader( "If-None-Match", jQuery.etag[ cacheURL ] );
    }
  }

  // Set the correct header, if data is being sent
  if ( s.data && s.hasContent && s.contentType !== false || options.contentType ) {
    jqXHR.setRequestHeader( "Content-Type", s.contentType );
  }

  // Set the Accepts header for the server, depending on the dataType
  jqXHR.setRequestHeader(
    "Accept",
    s.dataTypes[ 0 ] && s.accepts[ s.dataTypes[ 0 ] ] ?
      s.accepts[ s.dataTypes[ 0 ] ] +
        ( s.dataTypes[ 0 ] !== "*" ? ", " + allTypes + "; q=0.01" : "" ) :
      s.accepts[ "*" ]
  );

  // Check for headers option
  for ( i in s.headers ) {
    jqXHR.setRequestHeader( i, s.headers[ i ] );
  }

  // Allow custom headers/mimetypes and early abort
  if ( s.beforeSend &&
    ( s.beforeSend.call( callbackContext, jqXHR, s ) === false || completed ) ) {

    // Abort if not done already and return
    return jqXHR.abort();
  }

  // Aborting is no longer a cancellation
  strAbort = "abort";

  // Install callbacks on deferreds
  completeDeferred.add( s.complete );
  jqXHR.done( s.success );
  jqXHR.fail( s.error );

  // Get transport
  transport = inspectPrefiltersOrTransports( transports, s, options, jqXHR );

  // If no transport, we auto-abort
  if ( !transport ) {
    done( -1, "No Transport" );
  } else {
    jqXHR.readyState = 1;

    // Send global event
    if ( fireGlobals ) {
      globalEventContext.trigger( "ajaxSend", [ jqXHR, s ] );
    }

    // If request was aborted inside ajaxSend, stop there
    if ( completed ) {
      return jqXHR;
    }

    // Timeout
    if ( s.async && s.timeout > 0 ) {
      timeoutTimer = window.setTimeout( function() {
        jqXHR.abort( "timeout" );
      }, s.timeout );
    }

    try {
      completed = false;
      transport.send( requestHeaders, done );
    } catch ( e ) {

      // Rethrow post-completion exceptions
      if ( completed ) {
        throw e;
      }

      // Propagate others as results
      done( -1, e );
    }
  }

  // Callback for when everything is done
  function done( status, nativeStatusText, responses, headers ) {
    var isSuccess, success, error, response, modified,
      statusText = nativeStatusText;

    // Ignore repeat invocations
    if ( completed ) {
      return;
    }

    completed = true;

    // Clear timeout if it exists
    if ( timeoutTimer ) {
      window.clearTimeout( timeoutTimer );
    }

    // Dereference transport for early garbage collection
    // (no matter how long the jqXHR object will be used)
    transport = undefined;

    // Cache response headers
    responseHeadersString = headers || "";

    // Set readyState
    jqXHR.readyState = status > 0 ? 4 : 0;

    // Determine if successful
    isSuccess = status >= 200 && status < 300 || status === 304;

    // Get response data
    if ( responses ) {
      response = ajaxHandleResponses( s, jqXHR, responses );
    }

    // Convert no matter what (that way responseXXX fields are always set)
    response = ajaxConvert( s, response, jqXHR, isSuccess );

    // If successful, handle type chaining
    if ( isSuccess ) {

      // Set the If-Modified-Since and/or If-None-Match header, if in ifModified mode.
      if ( s.ifModified ) {
        modified = jqXHR.getResponseHeader( "Last-Modified" );
        if ( modified ) {
          jQuery.lastModified[ cacheURL ] = modified;
        }
        modified = jqXHR.getResponseHeader( "etag" );
        if ( modified ) {
          jQuery.etag[ cacheURL ] = modified;
        }
      }

      // if no content
      if ( status === 204 || s.type === "HEAD" ) {
        statusText = "nocontent";

      // if not modified
      } else if ( status === 304 ) {
        statusText = "notmodified";

      // If we have data, let's convert it
      } else {
        statusText = response.state;
        success = response.data;
        error = response.error;
        isSuccess = !error;
      }
    } else {

      // Extract error from statusText and normalize for non-aborts
      error = statusText;
      if ( status || !statusText ) {
        statusText = "error";
        if ( status < 0 ) {
          status = 0;
        }
      }
    }

    // Set data for the fake xhr object
    jqXHR.status = status;
    jqXHR.statusText = ( nativeStatusText || statusText ) + "";

    // Success/Error
    if ( isSuccess ) {
      deferred.resolveWith( callbackContext, [ success, statusText, jqXHR ] );
    } else {
      deferred.rejectWith( callbackContext, [ jqXHR, statusText, error ] );
    }

    // Status-dependent callbacks
    jqXHR.statusCode( statusCode );
    statusCode = undefined;

    if ( fireGlobals ) {
      globalEventContext.trigger( isSuccess ? "ajaxSuccess" : "ajaxError",
        [ jqXHR, s, isSuccess ? success : error ] );
    }

    // Complete
    completeDeferred.fireWith( callbackContext, [ jqXHR, statusText ] );

    if ( fireGlobals ) {
      globalEventContext.trigger( "ajaxComplete", [ jqXHR, s ] );

      // Handle the global AJAX counter
      if ( !( --jQuery.active ) ) {
        jQuery.event.trigger( "ajaxStop" );
      }
    }
  }

  return jqXHR;
}

So yeah, this is obviously ridiculous to try to remove all the dependencies from this code. You're better off just including jQuery if you want to use jQuery's method for loading external scripts asynchronously.

所以是的，试图从这段代码中删除所有依赖项显然是荒谬的。如果您想使用 jQuery 的方法异步加载外部脚本，最好只包含 jQuery。

Or, consider using a different tool altogether.

或者，考虑完全使用不同的工具。

---

---

July 16, 2013- from jQuery guts with no dependencies^{[source code citation needed]}

2013年7 月 16 日- 来自没有依赖项的 jQuery 胆量^{[需要引用源代码]}

function getScript(src, callback) {
  var s = document.createElement('script');
  s.src = src;
  s.async = true;
  s.onreadystatechange = s.onload = function() {
    if (!callback.done && (!s.readyState || /loaded|complete/.test(s.readyState))) {
      callback.done = true;
      callback();
    }
  };
  document.querySelector('head').appendChild(s);
}

回答by Interrobang

One of the best patterns to use here is to use addEventListenerto listen for a custom event such as "MyScriptLoaded". Then, modify your included script to fire this event as its last action. This will ensure that you take action only after the new script has fully loaded.

此处使用的最佳模式之一是addEventListener用于侦听自定义事件，例如“MyScriptLoaded”。然后，修改您包含的脚本以触发此事件作为其最后一个操作。这将确保您仅在新脚本完全加载后才采取行动。

回答by Jake Feasel

If you have control over the source of the javascript that gets loaded, your best bet would be to have that code execute a pseudo-callback function that exists within your page context. This is something like the method used for JSONP. So, imagine on your calling page, you have this:

如果您可以控制加载的 javascript 的源代码，最好的办法是让该代码执行页面上下文中存在的伪回调函数。这类似于用于 JSONP 的方法。所以，想象一下在你的呼叫页面上，你有这个：

function createScript(src, id) {
    if (document.getElementById(id) == null) {
        var newScript = document.createElement('script');
        newScript.setAttribute("type", "text/javascript");
        newScript.setAttribute("src", src);
        newScript.setAttribute("id", id);
        document.getElementsByTagName("head")[0].appendChild(newScript);
    }
}

function callbackFunc()
{
  // make use of new functions here....
}

And each of your source files might end with this line:

您的每个源文件都可能以这一行结尾：

callbackFunc();